Fluoropolymers are typically prepared by radical polymerization process; emulsion techniques wherein polymerization is effected in an aqueous medium in the presence of a surfactant in the presence of radical initiator for providing a stable dispersion or latex of fluoropolymer particles in water are particularly effective.
Over the past decade, various controlled radical polymerization techniques have been developed. Among these reversible addition-fragmentation chain transfer (RAFT) and macromolecular design via inter-exchange of xanthate (MADIX) have provided an advantageous route to so-called living polymerization processes, see for instance PERRIER, S., et al. Macromolecular design via Reversible Addition-Fragmentation Chain Transfer (RAFT)/Xanthates (MADIX) polymerization. J. Polym. Sci.: Part A: Polym. Chem. 2005, vol. 43, p. 5347-5393.
RAFT/MADIX agents are capable to act as a reversible chain transfer agent in free-radical polymerizations, thereby inducing reversible-addition fragmentation transfer reactions to create an equilibrium between propagating radicals (i.e. the growing polymer chain) and so-called dormant species (containing the chain transfer agent fragment) that can become active again.
The use of RAFT or MADIX controlled radical polymerization agents, hereinafter referred to as “RAFT/MADIX agents”, has been disclosed for instance WO 98/058974 A (RHODIA CHIMIE) 30 Dec. 1998 and WO 98/01478 A (E.I. DUPONT DE NEMOURS AND COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANIZATION) 15 Jan. 1998.
RAFT/MADIX agents have been proposed for use in emulsion polymerization techniques (see for instance U.S. Pat. No. 677,513 (RHODIA CHIMIE) 17 Aug. 2004); yet, U.S. Pat. No. 7,317,050 (RHODIA CHIMIE) 8 Jan. 2008 discloses a method for manufacturing block copolymers by emulsion polymerization in the presence of RAFT/MADIX agents from ethylenically unsaturated monomers, including possibly fluorinated monomers.
Nevertheless, when adding RAFT/MADIX agents in emulsion polymerization of fluorinated monomers in order to control microstructure of the polymer and introducing end-groups of formula —S—C(S)—Z, the reaction rate is so detrimentally affected, that controlled polymerization method is no actual utility.
There is hence a current shortfall in the art for an emulsion polymerization method under the control of RAFT/MADIX agent which is effective for the manufacture of fluoropolymers.